DEV: Refactor the Automation Plugin UI to match admin UI guidelines (#31060)

This change updates the Automation plugin to make use of the `use_new_show_route` plugin flag, as well as generally updating the UI to match current admin UI guidelines. Notable changes include:

- Moving template/router/controller files to make use of the `admin.adminPlugins.show` route.
- Changing the URIs from `/admin/plugins/discourse-automation` to `/admin/plugins/automation`, to match the `PLUGIN_NAME`.
- Adding UI wrappers around the New/Edit forms, and polishing the list of defined automations.

plugins/automation/config/routes.rb

@@ -10,13 +10,13 @@ DiscourseAutomation::Engine.routes.draw do
     put "/append-last-checked-by/:post_id" => "append_last_checked_by#post_checked"
   end
 
-  scope "/admin/plugins/discourse-automation",
+  scope "/admin/plugins/automation",
         as: "admin_discourse_automation",
         constraints: AdminConstraint.new do
     scope format: false do
-      get "/" => "admin#index"
-      get "/new" => "admin#new"
-      get "/:id" => "admin#edit"
+      get "/automation" => "admin#index"
+      get "/automation/new" => "admin#new"
+      get "/automation/:id" => "admin#edit"
     end
 
     scope format: :json do